1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Algebra Problem

  1. Oct 21, 2007 #1
    Can't figure out how the example in the book is getting from one step to the next.

    Here's the problem
    2(8+216/x)(-216/x^2) + 2(x+27) = 0

    The next step
    (x+27)(1-1728/x^3) = 0

    First thing I did was divide out the two & got
    (8+216/x)(-216/x^2) + (x+27) = 0
    Then I multiplied out the left part
    -1728x^-2 + 46656x^-3 + (x+27) = 0
    This got me nowhere it seems.
    Then I tried to find a common denominator
    -1728x-46656/x + (x+27) = 0
    this is what I got when I multiplied it out & still nowhere it seems. Any help would be appreciated.
  2. jcsd
  3. Oct 22, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Nope. This is wrong, so all that follows is also wrong.

    Next step:

    [tex] \frac {- 8 (216)} {x^2} - \frac {216^2} {x^3} + (x+27) =0 [/tex]

    now multiply through by [itex] x^3 [/itex] to get:
    [tex] -8(216)x - 216^2 + x^3 (x+27) = 0 [/tex]
    now you should be able to continue.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook